Perforating gun assembly

ABSTRACT

A perforating gun assembly includes a gun carrier and a gun connected thereto. The perforating gun is positioned external to a flow passage of the perforating gun carrier. The perforating gun is activated by pressure in the flow passage defined by the perforating gun carrier. The perforating gun may be positioned in a slot or pocket defined in a wall of the perforating gun carrier.

CROSS REFERENCE TO RELATED APPLICATION

This application incorporates by reference and claims the benefit of U.S. Provisional Application 61/858,485 filed on Jul. 25, 2013.

BACKGROUND

There are a number of different operations performed during the drilling and completion of subterranean wells. One such operation, referred to as perforating, is used to perforate well casing through the perforations. Casing is perforated adjacent formations, and zones in formations so that fracturing fluid may be pumped through the casing. After perforating and fracturing operation, fluid may be produced from the formation or zone. There are a number of perforating tools and methods utilized throughout the industry. For example, fluid jets may be used to perforate. Perforating guns are also used. Perforating guns may be lowered in on a wireline, detonated and then retrieved. Perforating guns may also be lowered in on tubing and retrieved after firing, or released to fall to the bottom of the well. While such methods work, often multiple trips into the well are required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are an elevation view of the gun assembly of the current disclosure.

FIGS. 2A and 2B are cross-sectional views showing the gun assembly of the current disclosure.

FIGS. 3 and 4 are views of the connections for the gun of the gun assembly.

FIGS. 5A and 5B are a cross-sectional view of a hydraulic delay assembly used in an embodiment for a perforating gun assembly.

FIG. 6 is a cross section of the upper portion of the gun assembly.

FIG. 7 is a cross section of a portion of the hydraulic delay assembly.

FIG. 8 is an elevation view of the gun carrier of FIG. 7.

FIG. 9 is a cross-sectional view of the gun carrier.

FIG. 10 is a cross section from line 10-10 of FIG. 9.

FIG. 11 is a cross sectional view of a firing head of the current disclosure.

FIG. 12 is a schematic view of a casing string including the perforating gun assembly of the current disclosure lowered into a well.

FIG. 13 is a perspective view of an additional embodiment of a perforating tool.

FIG. 14 is an exploded view of the tool of FIG. 13.

FIG. 15 is an exploded view of the upper portion of the embodiment of FIG. 13

FIG. 16 a front view of the tool of FIG. 13

FIG. 17. is a cross section from line 17-17 of FIG. 17.

FIG. 18 is a partial cross section of the tool of FIG. 13.

FIG. 19 is a cross section of a Y-block connection of the tool of FIG. 20.

FIG. 20 is a side view of an additional embodiment of a perforating tool.

FIG. 21 is a cross section from line 21-21 of FIG. 20.

SUMMARY OF THE INVENTION

The current disclosure is directed to a tool for perforating a well. The tool may be carried into the well on a casing string and may form a part of the casing string. The tool includes a gun carrier defining a central flow passage therethrough and a perforating gun positioned external to the flow passage of the perforating gun carrier.

The perforating gun is actuated by pressure applied through a flow passage of the casing string and the flow passage defined by the gun carrier. A removable barrier, for example a rupture disc, is positioned in a flow port that will connect the central flow passage of the gun carrier with a chamber external to the central flow passage. The chamber may be referred to as a detonation chamber since the application of pressure thereto will cause the firing of the perforating gun to perforate the casing and perforate a cement sheath adjacent the zone to be produced. The application of a predetermined pressure will cause the rupture disc to burst or will otherwise remove the removable barrier. The continued application of pressure will increase pressure in the detonation chamber to the required pressure to cause the perforating gun to detonate.

In one embodiment, a time delay is included. The time delay, which may be a hydraulic delay assembly, may comprise an upper chamber and lower chamber with a removable barrier such as a rupture disc therebetween. The upper and lower chambers may comprise part of the detonation chamber. Application of pressure to the upper chamber will cause the removal of the barrier between the upper and lower chambers, for example by rupturing the rupture disc. A nozzle may be included between the upper and lower chambers such that there will be a delay in filling the lower chamber with sufficient fluid to apply adequate pressure to detonate the perforating gun. A firing pin used to detonate may be held in place by shear pins or other means such that a predetermined application of pressure or force thereto will move the firing pin and cause the detonation of the perforating gun.

In one embodiment, the perforating gun is positioned in a pocket or slot defined in a wall of the gun carrier. The flow passage defined by the gun carrier may be an eccentric flow passage wherein the longitudinal central axis of the flow passage is offset from the longitudinal central axis of the gun carrier and the longitudinal axis of the casing string. The gun assembly which comprises the gun carrier and the perforating gun is concentric with the casing string. In an additional embodiment the slot or pocket includes more than one gun and may include two guns. The perforating guns may be positioned in parallel spaced relationship. In other words, the pair of perforating guns may be positioned side by side such that the longitudinal axes of the pair are parallel and spaced apart.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The current disclosure is directed to a downhole tool 10 connected in a casing string 12. Downhole tool 10 may be referred to as a gun assembly 10. As is known in the art, casing string 12 is made up of a plurality of casing joints 14. Casing joints 14 above and below gun assembly 10 have an outer diameter 16 and define a flow path 18 therethrough. Casing string 12 defines a longitudinal central axis 22.

FIG. 12 schematically shows casing string 12 with gun assembly 10 in wellbore 24. Wellbore 24 in the embodiment shown has horizontal portion 26 , vertical portion 28 and heel 30 connecting portions 26 and 28. An annulus 32 is defined by and between wellbore 24 and casing 12. Casing 12 may be cemented in the well by any means known in the art.

Gun assembly 10 includes a perforating gun 40 and a gun carrier 42. Gun 40 may be a perforating gun of a type known in the art. A firing head assembly 46, which may be a direct pressure firing head of a type known in the art, for example, a Hunting Titan direct pressure firing head is included to activate gun 40. Firing head assembly 46 includes a detonator 45 and firing pin 47.

Gun assembly 10 has a longitudinal central axis 48 which is collinear with longitudinal central axis 22 of casing 12. Gun carrier 42 has outer surface 49. An outer periphery, or circumference 50 is defined by an outer diameter 51 of gun carrier 42. Gun carrier 42 has upper end 52 and lower end 54 which are likewise the upper and lower ends of the gun assembly 10. Gun carrier 42 defines a carrier flow passage 56 therethrough that has longitudinal central axis 58. Longitudinal central axis 58 is offset from longitudinal central axes lines 22 of casing 12 and 48 of gun assembly 10. As such, flow passage 56 may be referred to as an offset or eccentric flow passage 56. As is apparent from the drawings, flow passage 56 is in fluid communication with flow path 18. In order to cement casing string 12 which includes gun assembly 10 in wellbore 24, cement is pumped through casing 12 and gun assembly 10 and will pass through casing 12 into the annulus 32. As will be described in more detail hereinbelow, after the cement is set, gun assembly 10 may be actuated with fluid pressure inside flow passage 56 to perforate the casing and cement sheath around the casing into a zone, or formation of interest.

Gun carrier 42 has a carrier slot or carrier pocket 62 defined therein for receiving perforating gun 40. Pocket 62 is defined in a wall 63 of gun carrier 42 and may have upper end 64, lower end 66 and a depth 68. Pocket 62 has an arcuate surface 70. Firing head assembly 46 is likewise positioned in carrier pocket 62. Firing pin 47 may be held in place by shear pins 69 such that when adequate pressure to overcome the shear pins is achieved the firing head assembly 46 will initiate firing of the perforating gun 40.

A hydraulic delay assembly 74 may also be positioned in carrier pocket 62. Although the embodiment described herein utilizes hydraulic delay assembly 74, it is understood that the gun assembly 10 may be utilized without a hydraulic delay. Hydraulic delay assembly 74 is connected to a pup joint 76 which in turn is connected to firing head assembly 46. Gun 40, hydraulic delay assembly 74 and firing head assembly 46 may also be positioned in the carrier pocket 62 such that outer periphery 50 defined by diameter 51 circumscribes gun 40, hydraulic delay assembly 74 and firing head assembly 46. In other words gun 40, delay assembly 74 and firing head assembly 46 lie within the periphery defined by the gun carrier outer diameter 51.

Hydraulic delay assembly 74 includes a delay housing 78 defining a delay chamber 80. Delay chamber 80 is defined in part by pup joint 76. Delay housing 78 has a lower end 82 and upper end 84. A piston housing 88 defines a piston chamber 90, and has an upper end 92 and a lower end 94. A piston 96 sealingly engages piston chamber 90. Piston chamber 90 is filled with fluid of known thermal properties which may be for example a silicone fluid. Piston chamber 90 and delay chamber 80 may be referred to collectively as a detonation chamber and piston housing 88 and delay housing 78 may be referred to collectively as a detonation housing. Piston 96 has 0-rings 100 therein to seal against surface 98 of piston chamber 90. A coupling 102 is connected to the lower end 94 of piston housing 86 and upper end 84 of delay housing 78. Coupling 102 has a nozzle 104 therein positioned between delay chamber 80 and piston chamber 90. Nozzle 104 has first passageway 106 with inner diameter 108 and second passage 110 with diameter 112. Passage 110 may be referred to as a jet 110. The diameter 112 of jet 110 is such that it will slow the rate of fluid flow into delay chamber 80 from piston chamber 90. A rupture disc 114 separates piston chamber 90 and delay chamber 80 and will burst at a predetermined pressure to allow fluid from piston chamber 90 into delay chamber 80.

A fitting 115 is threadedly connected to piston housing 86. Fitting 115 has a hollow stem 116 with a fitting flow passage 118. A rupture disc 120 is positioned in a flow port 122. Fluid may be communicated through flow passage 56 of carrier 42 through the flow port 122 when rupture disc 120 is ruptured. A clamp which may be an arcuate or curved clamp 124 is attached with fasteners or other means to carrier 42 and will hold the fitting 115 and thus gun 40 in place. Surface 126 of clamp 124 is concentric with and is preferably in alignment with outer surface 49 of gun carrier 42. Clamp 124 may be connected with screws or other connectors known in the art. A plug 130 may be connected to the lower end of gun 40. Plug 130 has a stem 132 which is held in place by clamp 134. Thus, clamps 134 and 124 hold perforating gun 40 in place.

Gun assembly 10 as described provides apparatus and methods for perforating a wellbore with no obstructions in the flow passage defined by the casing. In addition, it is not necessary with tool 10 to make multiple trips into the casing to perforate since the perforating gun is positioned exterior to the flow passage and is carried into the well with casing 12. Although the perforating gun 40 is external to flow passage 56, fluid pressure in flow passage 56 is utilized to actuate the perforating gun 40 to perforate the cement sheath into a formation or zone and to perforate the wall 63 of gun carrier 42 such that fluid can be communicated therethrough. When used with the hydraulic delay assembly 74, tool 10 of the current disclosure allows for a pressure test of casing 12 prior to activating the perforating gun.

For example, once casing 12 is cemented in wellbore 24 pressure may be increased in the flow passage 18 to 10,000 psi., or other desired test pressure. The test pressure, which is 10,000 psi in this example, is above the burst pressure of both of rupture discs 114 and 120. Disk 120 will rupture first, and the pressure applied through port 122 will move piston 96, which will push fluid in chamber 90 to rupture disk 114. The length and diameter of delay and piston chambers 80 and 90, along with the diameter of nozzle 104 and the fluid used in piston chamber 90 can be varied to provide the desired delay. The pressure may be held for a desired time to pressure test the casing 12. If casing 12 fails, pressure can be released so that the gun 40 is not actuated. Upon a successful test, pressure is maintained so that fluid will fill delay chamber 80. Continued application of pressure will actuate firing head assembly 46 and in turn perforating gun 40. Typically, the pressure at which the firing head assembly 46 will cause detonation is less than the casing test pressure and will be less the rupture pressure of discs 114 and 120. While the embodiment described herein is used with a hydraulic delay, it is understood that no hydraulic delay is necessary.

When gun assembly 10 is used without a hydraulic delay, there will be a rupture disc 120 in port 122 and there will be no barriers between port 122 and firing head assembly 46. The detonation chamber leading to firing head assembly 46 may have a piston therein so that application of fluid pressure through flow passage 56 will move the piston and create fluid pressure to activate firing head assembly 46. When pressure in flow passage 56 reaches the burst pressure of disk 120, continued application of pressure will cause firing head assembly 46 to actuate gun 40. The burst pressure of rupture disc 120 can be above the pressure test pressure to allow for pressure test of the casing prior to rupturing. Once ruptured, the pressure can be held at the pressure necessary to cause the firing head 46 to detonate and activate the perforating gun. In addition, the assembly can be utilized without a pressure test such that the rupture disc can be set to burst at a predetermined pressure below casing test pressure that will allow fluid to enter the chamber above the firing head and activate the gun.

While the disclosure herein describes only one gun assembly, it is understood that a plurality of gun assemblies may be longitudinally spaced in a casing string to provide perforations at multiple locations in the well. As is apparent, the use of gun assembly 10 eliminates the need for any coiled tubing runs and minimizes fracturing time. Gun assembly 10 can be adapted to any size casing and utilizes a standard cementing design and practices.

Because the gun assembly is concentric with the casing string, there is no overall eccentricity to the tool and the tool may be rotated to depth in the well bore with no damage.

In another embodiment shown in FIG. 13, a tool, or gun assembly 200 comprises a gun carrier 202 and a pair of perforating guns 204 which comprise first and second guns 206 and 208. First gun 206 has upper end 210, lower end 212, outer diameter or outer periphery 214 and a longitudinal central axis 216. Second gun 208 has upper end 218, lower end 220, outer diameter or periphery 222 and longitudinal central axis 224.

Gun carrier 202 is a generally tubular joint with an outer diameter or periphery 226 and a carrier flow passage 228 defined therethrough. Flow passage 228 is an eccentric flow passage since a longitudinal center axis 230 thereof is offset from the longitudinal central axis 231 of the gun carrier 206. Axes 230 and 231 are perpendicular to the plane of the page as shown in FIG. 17. Slots or pockets 232, 233 a and 233 b are defined in gun carrier 202 in a wall 235 thereof.

Guns 206 and 208 are positioned in slots 233 a and 233 b respectively, which may be referred to as gun slots 233 a and 233 b. The outer diameter or periphery 214 and 222 of guns 206 and 208, respectively, may fall inside or slightly outside, or tangent to the outer diameter 226 defined by gun carrier 202. Preferably, the perforating guns 206 and 208 lie inside the circle defined by periphery 226. First and second guns 206 and 208 are preferably positioned side by side. Longitudinal central axes 216 and 224 of guns 206 and 208, respectively, are parallel and are spaced apart. Thus, the guns may be described as in a parallel spaced relationship.

A fitting 115 like that described with respect to the embodiment of FIG. 1 herein may be mated with gun carrier 202 in the same manner as described with respect thereto and shown in FIG. 7. Thus, longitudinal central flow passage 228 will communicate through a flow port 122 once adequate pressure to rupture disc 122 is reached in flow passage 228. Fluid will thus be communicated into the fitting flow passage 118.

FIG. 13 depicts a slightly different arrangement which may be used with the embodiment of FIG. 1 as well. A clamp, or block 234 has arcuate outer surface 236 and a flat surface 238. The arcuate surface 236 has a radius of curvature that is the same as the radius of curvature of the gun carrier 202. Thus, when connected, the assembly has a circular outer diameter at the location of clamp 234. Gun carrier 202 has an upper cutout, or cutaway section 240 that defines a flat 242.

Clamp 230 has a rupture disc assembly 120 received in an opening therein. Gun carrier 202 defines a flow port 244. Clamp 234 defines a longitudinal passage 246 that will communicate with flow passage 228 when rupture disc 120 ruptures. Clamp 234 is connected to a detonation housing 248 which defines a detonation chamber 250 into which fluid flows. Detonation housing 248 may be like detonation housing 88 as described herein. Detonation housing 248 is positioned in slot 232. A piston 252 may be positioned in detonation chamber 250. In the embodiment described, the tool 200 is utilized without a hydraulic delay. Thus, pressure will act directly on a firing head assembly to detonate both of perforating guns 206 and 208. It is understood that hydraulic delay may be used as well.

In the embodiment of FIG. 13, the detonation housing 248 has upper end 254 and lower end 256. Upper end 254 is threadedly connected to clamp 234 such that detonation chamber 250 is communicated with the longitudinal fluid passage 246 in clamp 234.

Lower end 256 is connected to one or more pup joints 76 which will define a portion of detonation chamber 250, and which connect to firing assembly 46. Firing assembly 46 is threadedly connected to a center clamp 258. Center clamp 258 has arcuate outer surface 260 and a flat surface 262. Center clamp 258 will nest in cutaway 264 which defines flat 266 to mate with surface 262.

FIG. 18 is a section through center clamp 258. As shown therein detonator 45 of firing head 46 is connected by threading or other known means to center clamp 258. Center clamp 258 has cord passages 268 and 270. A detonator cord splits into cords 269 and 271 will pass through passages 268 and 270 and into upper ends 210 and 218 of perforating guns 206 and 208. Perforating guns 206 and 208 are adapted to be threadedly connected to center clamp 258.

A bottom clamp 272 having arcuate outer surface 274 and a flat surface 276 holds lower ends 212 ands 220 of perforating guns 206 and 208 in place. Clamp 272 will mate with flat surface 278 defined by cutaway 280 in gun carrier 202. Thus, when connected to gun carrier 202, clamp 272 mates therewith to define a circular cross section with a diameter matching the outer diameter of gun carrier 202.

Plugs 282 and 284 connected at lower ends 212 and 220 of guns 206 and 208 may be received in and connected to openings in bottom clamp 272. Guns 206 and 208 are positioned in slots 233 a and 233 b respectively in gun carrier 202. The guns preferably fall at or inside the circular periphery of the gun carrier 202. Upper, center and bottom clamps 234, 258 and 272 may be connected with fasteners to carrier 202.

In the embodiment of tool 200, pressure will be applied in the flow passage 228 to cause rupture disc 120 to rupture. Continued application of pressure will cause firing head assembly 46 to actuate such that it moves firing pin 47. In the embodiment shown, the detonator cord branches into first and second cords 269 and 271 which will cause detonation of each of guns 206 and 208 which will fire simultaneously.

It is understood that in each of the embodiments described herein, several gun assemblies may be longitudinally spaced along the casing such that a number of different locations can be simultaneously perforated. Thus, a number of different zones may be perforated and fractured without the necessity of more than one trip into the well.

In an additional embodiment identified as tool 300, shown in FIG. 20, a casing joint 302 has upper end 304, lower end 306 and defines a flow passage 308. An upper Y-block fitting 310 and a lower Y-block fitting 312 attach a perforating gun 314 to casing 302. Perforating gun 314 is external to flow passage 308. In the arrangement shown, gun 314 is positioned above the actuator or firing head 316 which may be like firing head 46 as described previously.

A detonation housing 318 defining a detonation chamber 320 is connected to actuator 316. A piston 321 may be positioned in detonation or piston housing 318. Flow port 322 may be defined in a wall 323 of lower Y-block 312. A rupture disc or other removable barrier 324 may be placed in flow port 322. Centralizer fittings 326 are utilized to center the tool 300 in the well in which it is placed, such as for example wellbore 24.

The operation of the embodiment of FIG. 19 is like that as previously described. In other words, an increase in pressure to a predetermined pressure in flow passage 308 will cause rupture disc 324 to rupture and allow flow therethrough. Continued pressure applied to the desired pressure will cause the firing head assembly to actuate which will detonate gun 314 and perforate casing 302 along with wellbore 24.

Each of the embodiments may be used individually or in combination with other tools. Likewise, a plurality of each of the embodiments described herein may be utilized in a single casing string so that a number of formations and/or zones within a formation can be perforated simultaneously by the application of pressure in the casing string. 

What is claimed is:
 1. A gun assembly for perforating a well comprising: a gun carrier having a circular outer periphery, and defining a central flow passage therethrough; and a perforating gun positioned in a pocket defined in a wall of the gun carrier.
 2. The gun assembly of claim 1 comprising the wall of the gun carrier defining two gun pockets for carrying perforating guns, the gun assembly comprising a perforating gun in each of the gun pockets.
 3. The gun assembly of claim 2 wherein the two perforating guns are positioned in parallel spaced relationship.
 4. The gun assembly of claim 2 further comprising a casing string for lowering the gun assembly into the well, the gun assembly having a longitudinal central axis that is colinear with a longitudinal central axis of the casing string.
 5. The gun assembly of claim 1, wherein the gun assembly is adapted to be lowered into a well and centrally located in the well.
 6. The gun assembly of claim 1 wherein the perforating gun is activated by the application of fluid pressure in the carrier flow passage.
 7. The gun assembly of claim 6 further comprising a hydraulic delay assembly for delaying the activation of the gun after pressure in the carrier flow passage has reached the activation pressure.
 8. The gun assembly of claim 7, the hydraulic delay assembly comprising: an upper chamber; + a lower chamber; a removable barrier positioned between the upper and lower chambers; and a piston positioned in the upper chamber, an upper chamber wall having a passage defined therein for communicating fluid from the carrier flow passage into the upper chamber.
 9. The gun assembly of claim 6, a gun carrier wall having a port defined therein for communicating fluid therethrough into a chamber positioned outside the gun carrier wall, further comprising a removable barrier located to prevent flow through the port until a predetermined pressure in the carrier flow passage is reached, and wherein the continued application of pressure after the removable barrier is removed will activate the perforating gun.
 10. A downhole tool comprising: a tubular joint defining a flow passage therethrough; and a perforating gun mounted to the joint and positioned external to the carrier flow passage in the tubular joint, wherein the application of fluid pressure in the flow passage will activate the perforating gun.
 11. The downhole tool of claim 10, the flow passage in the tubular joint comprising an eccentric flow passage, and wherein the perforating gun is positioned in a slot defined in a wall of the tubular joint.
 12. The downhole tool of claim 11, wherein two perforating guns are positioned in the slot.
 13. The downhole tools of claim 12, wherein the guns are positioned side by side in the slot.
 14. The downhole tool of claim 11 further comprising a casing string, the tubular joint being connected in the casing string, wherein the tubular joint is concentric with the casing string.
 15. The downhole tool of claim 11 further comprising a detonation housing disposed external to the flow passage in the tubular joint, the detonation housing defining a detonation chamber, the wall of the tubular joint having a port therethrough to communicate fluid from the eccentric flow passage to the detonation chamber, wherein the perforating gun is detonated as a result of fluid communicated into the detonation chamber from the eccentric flow passage.
 16. The downhole tool of claim 15, the detonation chamber comprising: an upper chamber; a lower chamber; and a removable barrier positioned between the upper and lower chambers, the barrier being rupturable upon the application of fluid pressure resulting from fluid flow into the detonation chamber from the eccentric flow passage.
 17. The tool of claim 16 further comprising a nozzle positioned between the upper and lower chambers.
 18. The tool of claim 16, further comprising a piston in the upper chamber, wherein fluid flow from the flow passage urges the piston towards the lower chamber, the upper chamber being filled with fluid below the piston.
 19. A tool for perforating a well comprising: a casing string positioned in the well, ; and a gun assembly connected in the casing string, the gun assembly comprising: a carrier defining a carrier flow passage therethrough; and a gun positioned in a slot defined in the carrier wall external to the flow passage, wherein the gun assembly is concentric with the casing joint.
 20. The tool of claim 19, wherein the carrier flow passage is an eccentric flow passage.
 21. The tool of claim 19, wherein the gun is a pressure activated gun, and wherein the gun is activated by fluid pressure applied in the carrier flow passage.
 22. The tool of claim 21, further comprising: a detonation housing connected to the gun, the detonation housing defining a detonation chamber; a wall of the carrier defining a flow port communicating the carrier flow passage with the detonation chamber; and a removable barrier positioned to block communication through the flow port, wherein the barrier is removable upon application of a predetermined pressure to allow communication therethrough and wherein the gun will detonate upon the application of pressure in the carrier flow passage.
 23. The tool of claim 19 wherein the carrier defines a pair of gun slots for receiving perforating guns, further comprising a perforating gun positioned in each slot.
 24. The tool of claim 23, the pair of guns having parallel, spaced longitudinal central axes.
 25. The tool of claim 24, wherein the detonation housing is positioned in a slot located above the gun slots. 